Conventional luminaires used in lighting systems are generally classified as direct or indirect lighting fixtures. Direct lighting shines directly on a surface, such as a desktop or work surface, without being reflected from another surface. Indirect lighting is ambient lighting that is reflected from another surface such as a ceiling before impinging on the lighted area or surface. More recently, hybrid type fixtures have been developed that include both direct and indirect lighting characteristics. Such lights may be specified with the percentage of direct/indirect light characteristics, for example, 65%/35%, where 65% is the portion of indirect and 35% the portion of direct, of the total light emitted by the fixture. These ratios are generally achieved using fluorescent lighting tubes that emit light equally in all directions.
The light distribution ratio between direct and indirect is accomplished through the geometry of the fixture in which the fluorescent tubes are mounted. Diffusers and parabolic reflectors are positioned below the fluorescent tubes to reflect portions of the downwardly directed light, which is then reflected to the ceiling. Ceilings normally have an irregular surface that further diffuses and scatters the light, rather than directly reflecting the light. The percentage of indirect to direct light may be designed with more or less direct light. Once the light distribution profile of a luminance is set in the manufacturing stage it is not capable of being varied without disassembling and rebuilding the entire fixture with different components.
U.S. Pat. No. 6,789,914 discloses a luminance that provides both direct and indirect lighting through elongated reflecting members and a main reflector for delivering a uniform illumination. Each reflecting member is a louver extending along the luminance sides and the main reflector extends between the luminance sides. The luminance reflects light directly and indirectly to furnish a uniform illumination without undesirable hot spots and glare.
U.S. Pat. No. 6,843,586 is directed to a luminance having a concave reflector suspended from the ceiling. The reflector is positioned directly in the path of the light. The light is shielded from the reflector and diffused by being reflected onto the walls and ceiling. A reflector dome may be positioned above the light source and opposite the pendant reflector. The luminance redirects diffused light reflected by the pendant reflector while shielding a viewer from the intense light present at its point source.
U.S. Pat. No. 6,705,742 is directed to a system for directing light from a luminance. The luminance includes a source of light removably positionable in the luminance, a first reflecting device installed in the luminance for transmitting substantially indirect lighting from the luminance, a second reflecting device mounted in the luminance for transmitting substantially direct lighting from the luminance, and a fascia engageable with the luminance for emitting substantially luminous direct lighting. The luminance is useful for providing combinations and permutations of direct and indirect lighting.
Referring first to FIG. 1, an exemplary prior art luminance is generally designated as 10. A single lamp serving as a light source 12 is disposed between a louver portion 14 and a diffuser lens 16. Rays of light 20 are emitted radially from the light source 12 substantially uniformly in every direction. A portion of the light rays 20 emitted from the light source 12 are directed toward the ceiling 26. The upward light rays 20 penetrate the diffuser lens 16 and are spread or scattered by the diffuser lens 16 into a generally random pattern in the direction of the ceiling 26. The scattered light rays 20′ are then reflected from the ceiling 26 toward the area below the luminance 10, to provide the indirect component of the light distribution.
A portion of the light rays 20 emitted from the light source 12 are also directed toward the louver portion 14, as indicated by arrows 30 and 30′. The light rays 20 in the downward direction impinge on the louver portion 14 at various angles. The downward light rays 30, 30′ thus provide the direct component of the light distribution, and an additional portion of the indirect light distribution. Yet another portion of the light rays 20 are emitted horizontally, and do not impinge on either the diffuser portion 16 or the louver portion 14. This horizontally emitted portion of the light rays 20 accounts for ambient light in the general area.
The luminance shown in FIG. 1 is for illustration only, and many variations of these arrangements are known to those skilled in the art. For example, 2-, 4- or 8-lamp luminaires are commonly available, and the louver portions may be comprised of a variety of plastic lenses, parabolic reflectors, diffusers, and combinations thereof.
LED light sources offer several benefits over fluorescent systems, such as reliability, longer life, reduced heat dissipation, and reduced energy consumption, with little or no added weight. High voltage ballasts that are required to start the fluorescent tubes are not needed for LED light sources.
A light source made from LEDs is highly directional, focusing most light in one orientation as opposed to the continuous radial distribution of light around a fluorescent tube. The combination of mounting, location, filtering and distribution of white LEDs in a multi-LED design is critical to achieving an aesthetic light output. The directional nature of the diodes themselves creates a situation where a slight angular change in the installation can significantly change the appearance of lighted areas. As a result, the primary usage of LED light sources to date has been for commercial signage and architectural accent lighting, rather than general-purpose lighting. LEDs offer many advantages, including low power consumption, low heat dissipation and much longer life compared to traditional fluorescent and incandescent bulbs.
Therefore what is needed is a luminance that can have variable ratios of direct/indirect lighting without the need to change the geometry of the luminance.